IAS: PrEP Results Surprised Researchers

Action Points

Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

Explain that HIV-negative heterosexual partners of HIV-infected individuals were significantly less likely to acquire the virus if they were taking one of two antiretroviral drug regimens compared with placebo.

Point out that the results were striking enough that the placebo arm of the study was stopped early.

ROME – With only a few days until the opening of the 2011 meeting of the International AIDS Society, Jared Baeten, MD, PhD, and his colleagues were planning a couple of low-key poster presentations.

Then, on July 10th, the data safety monitoring board of the large HIV prevention study Baeten was leading dropped a bombshell, urging that early results be released and the placebo arm of the study be closed.

So, on the first full day of the conference, Baeten, of the University of Washington in Seattle, found himself in a press conference here, with his name hastily scrawled -- and misspelled – on a placard in front of him.

"We were just aware of these results eight days ago," Baeten said. "Hence the hand-written name tag."

The study – dubbed Partners PrEP – is one of two presented here showing that giving antiretroviral medication to HIV-negative heterosexual men and women can reduce the risk of acquiring the virus.

Baeten and colleagues had planned to present some minor early results from the study, but the data committee found that the approach – called pre-exposure prophylaxis, or PrEP – reduced the risk of HIV transmission by between 62% and 73%.

The effect was "overwhelming and clearly convincing," Baeten told reporters.

It's also part of an unprecedented flurry of positive prevention results, according to Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases.

"I have never seen something explode like this," Fauci told reporters, referring to the two PrEP studies and a third major study that showed full treatment of HIV-positive people dramatically cut their risk of transmitting the virus to their uninfected partners.

Earlier related results included evidence that a vaginal microbicide gel can be used by women to reduce their risk of getting HIV and a study of PrEP in a group of high-risk men who have sex with men.

The Partners PrEP study looked at 4,747 so-called "discordant couples" in which one partner did not have HIV and the other did, although the infected partner was not yet medically eligible for full triple-drug therapy. The uninfected partners were randomly assigned to get a daily dose of tenofovir (Viread), tenofovir plus emtricitabine (Truvada), or placebo.

As usual in such trials, all participants got a range of other prevention measures including counseling and free condoms.

After 36 months of follow-up, Baeten reported, the data monitoring committee found a total of 78 HIV infections among the initially uninfected participants – 18 among those getting tenofovir alone, 13 among those getting the combination pill, and 47 in the placebo arm.

Compared with placebo, he reported, tenofovir reduced the transmission risk by 62% and tenofovir/emtricitabine by 73%, differences that were significant at P=0.0003 and P<0.0001, respectively.

The effects of the different drugs were not statistically different from each other, he said. The effects were also similar among men and women.

The approach was also safe, Baeten said, with no significant differences from placebo in deaths, serious adverse events, or serious adverse laboratory values in creatinine or phosphorous.

On the other hand, after a month on the drug, participants taking tenofovir reported an increased risk of nausea, compared with placebo, while those on the combination pill reported a trend toward more nausea. At the same time, tenofovir/emtricitabine participants reported an elevated risk of diarrhea, compared with placebo, while those taking tenofovir alone also tended to report more of the condition.

One of the questions surrounding PrEP has been whether a false sense of security might promote an increase in risky sexual behavior, but that did not appear to be the case in this study, Baeten said.

At the start, 27% of the couples reported unprotected sex within the previous month, a figure that fell at a similar rate in all three arms during the follow-up, he reported. About a third of participants in all three arms reported an outside partner during the study.

The researchers are still analyzing data from those who acquired the virus to see if there are signs of drug resistance. The two drug arms of the study are continuing to see if there are important differences.

The study was supported by the Bill and Melinda Gates Foundation. Gilead Sciences donated the study drug. Baeten did not report any conflicts.

MedPageToday is a trusted and reliable source for clinical and policy coverage that directly affects the lives and practices of health care professionals.

Physicians and other healthcare professionals may also receive Continuing Medical Education (CME) and Continuing Education (CE) credits at no cost for participating in MedPage Today-hosted educational activities.